Brake squeal from wheel brake systems can be a frequent and annoying problem. These brake squeal problems can also occasionally cause costly accelerated wear and tear on a brake system and can affect both carbon and steel brakes.
Brake squeal is essentially a self-excited vibration in which the stationary parts of the brake oscillate torsionally about the wheel axle centerline. It can be experienced with aircraft brake systems as well as automotive braking systems. Brake squeal is closely tied to the friction properties of the brake lining material and, in particular, the relationship between friction coefficient and slip velocity. When the friction coefficient decreases with slip velocity, the friction forces become timed with the oscillating motion of the vibration, pushing the brakes further (i.e., torsionally about the axle) with each cycle. This can produce an unstable "squeal " vibration that grows in amplitude. Brake squeal is objectionable not only because of the loud, unpleasant noise generated, but also because of the accelerated wear that can be produced on the brake system if the degree of brake squeal produced is significant.
Brake squeal mitigation efforts have traditionally focused on changing the friction properties of the brake lining material used in the brakes. However, these efforts have tended to be trial and error efforts, and frequently have involved a tradeoff between limiting vibration levels and reducing brake wear properties. Other methods of attempting to reduce brake squeal include structurally stiffening the brakes, increasing friction damping and changing brake mass properties. The effects of these changes have proven to be of generally limited effectiveness, and a fine balance is required to achieve a stable brake which exhibits little or no brake squeal.
It is therefore a principal object of the present invention to provide a brake squeal attenuator that is capable of operating with existing aircraft wheel brake systems to eliminate, or substantially eliminate, brake squeal.
It is another object of the present invention to provide a brake squeal attenuator which can be easily retrofitted to existing aircraft wheel brake systems to entirely or substantially eliminate brake squeal.
It is still another object of the present invention to provide a brake squeal attenuator which can be added to an existing aircraft wheel brake system without significantly increasing the overall cost of the brake system and without requiring significant modifications to existing components of the brake system.